1. Field of the Invention
The present invention relates to a method and apparatus for controlling a motor actuator under drive mode, and to a recording medium storing a program for carrying out the method, and more particularly to improvements in accuracy of the control of motor actuators for driving air-conditioning doors used in a vehicle air-conditioning equipment and the like.
2. Description of the Relate Art
A conventional method of this kind is disclosed, for example, in Japanese Patent Publication No. Sho 59-43326 as a method for controlling a air-mixing door by means of a motor actuator of a vehicle air-conditioning equipment. The conventional method includes the steps of providing a so-called insensitive band area in the vicinity of a target opening angle and de-energizing the motor actuator when the air-mixing door reaches the in sensitive band area.
On the other hand, for example, Japanese Patent Laid-Open No. Sho 61-287809 discloses another method for controlling the air-mixing door by means of the motor actuator of the vehicle air-conditioning equipment. That method includes the steps of providing a so-called insensitive band area and a target opening angle in each of opposite sides of a standard opening angle of the air-mixing door and preventing the motor actuator from "hunting" in the vicinity of the standard opening angle of the air-mixing door to improve in control accuracy the motor actuator.
There is further another conventional method of this kind, as disclosed in Japanese Patent Publication No. Hei 8-2200. That method includes steps of detecting a difference between the number of drive pulses required by a drive circuit for a stepping motor forming a motor actuator and that of actual pulses received by the stepping motor, judging the difference in size with reference to a pair of standard values, and driving the stepping motor with a predetermined number of pulses depending on the result of this judgment. The number of the drive pulses is reduced when the number of the drive pulses required by the drive circuit varies violently, which improves the service life of the stepping motor.
As for the above-mentioned conventional method Patent Publication No. Sho 59-43326, when the motor forming the motor actuator is of a type suffering from a so-called overrunning so that the motor cannot stop immediately after the supply of a drive signal to the motor is cut, such overrunning makes it possible for the motor to reach its target position in a condition in which the supply of the drive signal to the motor is cut at a time when the motor reaches the insensitive band area of the target position. However, when the motor is of a type with no overrunning after the supply of the drive signal to the motor is cut, as with a stepping motor, the motor immediately stops when it reaches the insensitive band area, which produces a difference between the target position and its actual position. Since this difference corresponds in size to the insensitive band area, the motor cannot reach its target position. This is a problem inherent in the above one of the conventional methods.
On the other hand, as to the Japanese Patent Laid-Open No. Sho 61-287809 disclosing another conventional method, it is necessary to provide both the target opening angle and its insensitive band area in each of opposite sides of the standard target opening angle, which makes the entire system complicated. Further, in the case of the above-mentioned Japanese Patent Publication No. Sho 59-43326, its controlling accuracy depends on the overrunning properties of the motor actuator, which causes many problems when the motor actuator is constructed of a stepping motor.
This Japanese Patent Laid-Open No. Sho 61-287809 also discloses an apparatus for controlling the air-mixing door by means of the motor actuator of the vehicle air-conditioning equipment. In this apparatus, in order to avoid the problems described above, the motor actuator may be of a "no overrun" type. However, in this case, the insensitive band area is extremely reduced in width to substantially "zero", which forces the motor actuator to operate without stopping. Because, even, the slightest change in a signal representing the thermal environment, calculated in the vehicle air-conditioning equipment produces the drive signal being supplied to the motor actuator. Such restless operation (i.e., "hunting") of the motor actuator considerably reduces its services life, and produces harsh mechanical noise.
On the other hand, in an apparatus for carrying out the method disclosed in the Japanese Patent Publication No. Hei 8-2200, in contrast with the two above-mentioned conventional techniques, the motor actuator is controlled so as to gradually approach its target position. Consequently, the motor actuator requires much more time to reach the target position than the others, which impairs the apparatus in responsibility. Further, since this apparatus has no insensitive band area in contrast with the others, the apparatus has poor stability in operation. In order to improve the apparatus in this respect, a timer is used to prevent the apparatus from operating for a predetermined period of time so as to improve the apparatus in stability in operation. However, the use of such timer complicates the apparatus in construction.